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TPA2000D1TPWRQ1 Scheda tecnica(PDF) 10 Page - Texas Instruments |
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TPA2000D1TPWRQ1 Scheda tecnica(HTML) 10 Page - Texas Instruments |
10 / 22 page 0 V −5 V +5 V Current OUTP OUTN Differential Voltage Across Load 0 V −5 V +5 V Current OUTP OUTN Differential Voltage Across Load Output = 0 V Output > 0 V Efficiency: Why Use a Filter With the Traditional Class-D Modulation Scheme Effects of Applying a Square Wave Into a Speaker TPA2000D1-Q1 SGLS137E – SEPTEMBER 2002 – REVISED OCTOBER 2008 ........................................................................................................................................ www.ti.com Figure 10. The TPA2000D1 Output Voltage and Current Waveforms Into an Inductive Load The main reason that the traditional class-D amplifier needs an output filter is that the switching waveform results in maximum current flow. This causes more loss in the load, which causes lower efficiency. The ripple current is large for the traditional modulation scheme because the ripple current is proportional to voltage multiplied by the time at that voltage. The differential voltage swing is 2 × VDD, and the time at each voltage is half the period for the traditional modulation scheme. An ideal LC filter is needed to store the ripple current from each half cycle for the next half cycle, while any resistance causes power dissipation. The speaker is both resistive and reactive, whereas an LC filter is almost purely reactive. The TPA2000D1 modulation scheme has little loss in the load without a filter because the pulses are short and the change in voltage is VDD instead of 2 × VDD. As the output power increases, the pulses widen making the ripple current larger. Ripple current could be filtered with an LC filter for increased efficiency, but for most applications, the filter is not needed. An LC filter with a cut-off frequency less than the class-D switching frequency allows the switching current to flow through the filter instead of the load. The filter has less resistance than the speaker that results in less power dissipated, which increases efficiency. Audio specialists have advised for years not to apply a square wave to speakers. If the amplitude of the waveform is high enough and the frequency of the square wave is within the bandwidth of the speaker, the square wave could cause the voice coil to jump out of the air gap and/or scar the voice coil. A 250-kHz switching frequency, however, is not significant because the speaker cone movement is proportional to 1/f2 for frequencies beyond the audio band. Therefore, the amount of cone movement at the switching frequency is small. However, 10 Submit Documentation Feedback Copyright © 2002–2008, Texas Instruments Incorporated Product Folder Link(s): TPA2000D1-Q1 |
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